Safety devices which guard against injury or damage on escalators are well known in the art. These devices are commonly related to the moving hand rail, or to the moving treads on the escalator. Points on the escalator which typically require the use of such safety devices are the point where the handrail enters the fixed housing to reverse its direction of movement, and the point where the treads enter the fixed landing to reverse their direction of movement. Devices have been proposed and used at these points for either stopping the escalator or sounding an alarm should a foreign object pass between the hand rail and its housing, or the treads and the landing. Some of these prior art devices will reverse the escalator when actuated to attempt to dislodge the foreign body which has actuated the device. Most of the prior art safety devices utilize some sort of mechanical sensor which is caused to move by contact from the foreign body. Typically, the floor plate, or part of it, and the landing, may be pulled up by something passing underneath the comb of the landing. When this movement occurs, and electrical contact will be made or broken, and the escalator motor may stop, an alarm may sound, the escalator may reverse its direction, or a combination of the foregoing may occur.
The aforesaid mechanical actuators can be prone to a number of operational problems which may render them inoperable. For example, the foreign body passing beneath the comb may not exert enough force on the device to cause the required movement to occur, or it may not occur in good time. This might be the case were a scarf or other light fabric to run beneath the comb. Another problem which is known to occur in connection with these safety devices is that they cannot work if someone is standing on the part that is supposed to move. Thus if a person who has an article of clothing caught beneath a tread comb, or someone trying to help that person, is standing on the comb or on the part of the landing that must move to trigger the safety device, the device will not work. Finally, devices of this type can become fouled by material deposited on the treads, and thus may stick and not operate properly.